Adhesive and use thereof

ABSTRACT

Adhesives for bonding paper facings to aerated concrete provide increased manufacturing efficiencies and long term stability of constructs prepared therewith. Adhesives may advantageously be used in the foamed state.

FIELD OF THE INVENTION

[0001] The invention relates to an adhesive composition and to articlesof manufacture comprising the adhesive. Particularly preferredembodiments of the invention relate to a foamed adhesive and towallboard sheets comprising a concrete core material bonded to a facelayer with the foamed adhesive.

BACKGROUND OF THE INVENTION

[0002] Wallboard sheets are widely used in building construction toform, e.g., the walls and ceilings of rooms and the like. Such wallboardsheets generally comprise a gypsum core with outer face layers of paper,and are typically referred to as gypsum board, sheet rock or drywall.Gypsum wallboard is typically manufactured by delivering a slurry orpaste containing crushed gypsum rock onto a moving sheet of facing paperto which a second or top paper layer is then added to form a long boardline. The board line permits the slurry to harden before being cut. Thecut panels are heated in a kiln, before being packaged for storage andshipping. Typically, such sheets are ½ or ⅝ inch thick and inconventional sizes of 4×8 feet, and may weigh from about 55 to about 70pounds. Accordingly, handling of such gypsum wallboards presents asignificant task for construction personnel or wallboard “hangers”,particularly when such boards are secured overhead to form a ceiling. Inaddition, the fire resistance, thermal insulation and sound absorbingproperties of conventional gypsum wallboard sheets may not be sufficientfor some applications, such as walls between adjacent apartments.

[0003] The use of aerated concrete as the core material in wallboardsheeting is known and has been used successfully in countries outsidethe United States, including Europe and Japan. Published Internationalpatent WO 00/27866 describes a wallboard sheet comprising an aeratedconcrete core covered with outer face layers.

[0004] Aerated concrete is a steam cured mixture of sand or pulverizedfuel ash, cement, lime and an aeration agent. High pressure steam curingin an autoclave produces a physically and chemically stable product withan average density being about one fifth that of normal concrete. Thematerial includes non connecting air cells, and this gives aeratedconcrete some of it its unique and advantageous properties such as goodstrength, low weight (a 1 inch thick, 4 foot by 8 foot wallboard sheettypically has a total weight of about 60 pounds), good thermalinsulation properties, good sound deadening properties, and has a highresistance to fire. Aerated concrete has durability similar toconventional concrete or stone, has a thermal conductivity six to tentimes better than conventional concrete and is non-rotting, non-toxicand resistant to termites.

[0005] Like conventional sheet rock, aerated concrete sheets may bemanufactured to have beveled portions adjacent respective opposing sideedges, may be readily cut to size by first scoring the face sheet, andthen snapping the board about the score line, may be easily fastened toa suitable building frame, the seams between adjacent wallboards covered(taped and spackled) to provide an even wall surface, and may be paintedor, alternatively, covered with a decorative wall covering.

[0006] Aerated concrete provides advantages over conventional gypsumwallboard in terms of increased fire resistance, thermal insulation,sound deadening, and other properties, and, in addition, because of therelative light weight, substitution of aerated concrete for gypsumfacilitates, shipping, handling, and installation at a job site.

[0007] While wall sheet materials formed of aerated concrete cores offermany advantages over convention gypsum material, there continues to be aneed in the art for an adhesive useful for bonding paper face stockmaterial to aerated core material which is economical (i.e., will notadd significantly to the cost of the final wall sheet material) andwhich exhibits long term stability, a problem encountered in the priorart use of aerated concrete. The current invention fulfils this need inthe art by providing an adhesive formulation capable of increasingmanufacturing efficiencies and long term stability of constructsprepared therewith.

SUMMARY OF THE INVENTION

[0008] The invention provides an adhesive that is both economical, inparticular when used in its foamed state, and is capable of stabilybonding a paper face stock material to an aerated concrete corematerial.

[0009] The present invention relates to an adhesive and, in particular,to a foamed adhesive, as well as to articles of manufacture comprisingthe adhesive.

[0010] One aspect of the invention is directed to a water based adhesivecomprising ethylene vinyl acetate and/or propylene vinyl acetate, and apolyvinyl alcohol. The adhesive preferably also comprises at least onefiller such as clay. In a preferred embodiment the adhesive is foamed.

[0011] Another aspect of the invention is directed to an article ofmanufacture comprising the adhesive described herein. The articlecomprises a core material and a surface material, wherein the corematerial and surface material are bonded together with adhesive/foamedadhesive. In a preferred embodiment, the substrate material is concreteand the surface material is a paper stock material. In an even morepreferred embodiment, the core material is an aerated concrete material.Articles of manufacture encompassed by the invention include aeratedconcrete sheet materials.

[0012] A wallboard sheet of the invention comprises a core havingopposing first and second major surfaces; said core comprising aeratedconcrete; and at least one face layer on at least one of the first andsecond major surfaces of said core, wherein at least one of said facelayer is bonded to the core with the adhesive or the foamed adhesivedescribed herein.

[0013] Yet another aspect of the invention is directed to a method forbonding materials together which comprises applying the adhesive or thefoamed adhesive composition described herein to a first substrate,bringing a second substrate in contact with the adhesive compositionapplied to the first substrate, and subjecting the applied compositionto conditions which will allow the composition to cool and form a setbond. In a preferred embodiment, at least one of said substratescomprise a concrete material. In a particularly preferred embodiment,one substrate is an aerated concrete and one substrate is a paper stockmaterial.

DETAILED DESCRIPTION OF THE INVENTION

[0014] An adhesive has now been discovered that may be used to stabilybond paper stock materials to concrete, aerated concrete and the like.The adhesive may advantageously be used in the foamed state. By foaming,less water is introduced into the construction, the temperaturerequirements of the heaters may be decreased, and line speed may beincreased. The foamed adhesive when used in the practice of theinvention has sufficient wet bond strength for holding sheets of papermaterial to concrete panels as these panels are moved through a heatingand pressing zone.

[0015] The adhesives of the invention may be used to prepare variousarticles of manufacture, but are particularly useful in bonding paperface stock to aerated concrete panels in the preparation of wallboardsheet material.

[0016] The preparation of aerated concrete panels are known in the artand need not be described in detail herein. Reference is made topublished international application WO 00/27866.

[0017] Use of “paper” face stock includes paper and paperboard products,both single- and multi-ply (e.g., paper laminates) sheets made fromwithout limitation, Kraft paper, paper made from recycled fibers and thelike. The term face stock is used herein to refer to both face andbacker paper.

[0018] Adhesives of the invention comprise a vinyl acetate copolymer, apolyvinyl alcohol and, optionally, at least one filler. Typically, theadhesive will comprises from about 15% to about 50% by weight of thevinyl acetate component and from about 3% to about 7% by weight of thepolyvinyl alcohol component. Amounts of from about 2% up to about 30% byweight of the filler will generally be used. Other conventionaladditives, including preservative/biocides or the like may also beadded, with water added to total 100%.

[0019] Preferred for use are ethylene vinyl acetate or propylene vinylacetate or mixtures thereof. Ethylene vinyl acetate and propylene vinylacetate copolymers are well known commercially available materials.Exemplary techniques for their preparation are described in, for exampleU.S. Pat. Nos. 2,200,429 and 2,396,785. The percent of vinyl acetate inthe copolymer will generally range from about 4% to about 80% by weightand a melt index of about 0.1 to 1000 grams per minute. The vinylacetate copolymer typically will be alcohol or surfactant stabilized.

[0020] While ethylene vinyl acetate or propylene vinyl acetate ormixtures thereof may be use in the practice of the invention, the use ofethylene vinyl acetate has been discovered to be particularlyadvantageous in terms of long term stability of the adhesive bonds whenused to secure paper face stock material to a concrete or aeratedconcrete substrate. Thus, a preferred adhesive for use in the practiceof the invention will comprise ethylene vinyl acetate.

[0021] Ethylene vinyl acetate copolymers are available from DuPontChemical Co., Wilmington, Del. under the tradename Elvax® (e.g., Elvax®210 which has a melt index of 400 grams/10 minutes and a vinyl acetatecontent of 28% by weight in the copolymer, Elvax® 205W which has a meltindex of 800 and a vinyl acetate content of about 28% by weight in thecopolymer and Elvax® 410 which has a melt index of 500 and a vinylacetate content of about 18% by weight). Other ethylene vinyl acetatecopolymers are available from Exxon Chemical Co. under the tradenameEscorene® (e.g., UL 7505) and also from Millennium Petrochemicals,Rolling Meadows, Ill., under the tradename Ultrathene® (e.g., UE 64904)and AT® copolymers available from AT Polymers & Film Co., Charlotte,N.C. (e.g., AT® 1850M), and also from ATOFINA under the tradenameEvatane (e.g 28-420). Still others are available from National Starchand Chemical Company under the tradename DUR-O-SET®.

[0022] The polyvinyl alcohol for use in the invention will be at leastpartially hydrolyzed. By partially hydrolyzed means that the degree ofhydrolysis will be at least 87% or greater, preferably 89% or greater.Preferably, the polyvinyl alcohol will be fully hydrolyzed, i.e., thedegree of hydrolysis will be about 98.5% or greater. Polyvinyl alcoholis commercially available from Air Products, Celanese and Du Pont, amongothers.

[0023] Particularly preferred adhesives comprise ethylene vinyl acetate,a fully hydrolyzed polyvinyl alcohol, and at least one filler. In apreferred embodiment, the adhesive comprising ethylene vinyl acetate, afully hydrolyzed polyvinyl alcohol, and at least one filler, will be afoamed adhesive.

[0024] Suitable fillers are those fillers known in the art as adhesivesfillers and include polysaccarides, calcium carbonate, clay, mica, nutshell flours, silica, talc and wood flour. A clay filler may typicallybe used to prepare adhesives for use in the practice of the invention.The addition of a filler allows for foam generated to remain consistentand stable for several hours.

[0025] In addition to fillers, other additives typical of adhesivecompositions may be added to the foamable composition. Said additivesinclude, but are not limited to, plasticizers, acids, waxes, syntheticresins, tackifiers, defoamers, preservatives, bases such as sodiumhydroxide, dyes, pigments, UV indicators, and other additives commonlyused in the art.

[0026] The adhesive may also contain a surface-active agent. Examples ofsurface-active agents include anionic, cationic, amphoteric, or nonionicsurfactants, or mixtures thereof. Suitable anionic surfactants include,alkyl sulfonates, alkylaryl sulfonates, alkyl sulfates, sulfates ofhydroxylalkanols, alkyl and alkylaryl disulfonates, sulfonated fattyacids, sulfates and phosphates of polyethoxylated alkanols andalkylphenols, and esters of sulfosuccinic acid. Suitable cationicsurfactants include, alkyl quaternary ammonium salts, and alkylquaternary phosphonium salts. Suitable non-ionic surfactants include theaddition products of 5 to 50 moles of ethylene oxide adducted tostraight-chain and branched-chain alkanols having 6 to 22 carbon atoms,alkylphenols, higher fatty acids, higher fatty acid amines, primary orsecondary higher alkyl amines, and block copolymers of propylene oxidewith ethylene oxide, and mixtures thereof. When used, the surface activeagent will typically be added in amounts up to about 20% by weight,based on the foamable composition as a whole. More usually from amountsof from about 0.05 to about 20% by weight, and preferably at from 0.2 to2% by weight.

[0027] Preservatives for use herein include those conventionally used inaqueous adhesives such as benzoates, amides and fluorides such as sodiumfluoride. Also included are the hydroxybenzoic acid esters such asp-hydroxybenzoic acid methyl ester or p-hydroxybenzoic butyl ester.Commercially available preservatives which may be used in the practiceof the invention include KATHON LXE sold by Rohm & Haas Company andNipacide OBS sold by Clariant. The preservative will generally beincluded in amounts of from 0.05% to about 0.2% by weight.

[0028] The foamable adhesive composition of the invention is foamed bythe addition of energy, by means known in the art such as, but notlimited to, by mechanical and/or chemical means. Air or other gases areadded to the foamable adhesive composition along with the addition ofsaid energy to produce a stable, consistent foamed adhesive. Preferablyair is used to produce the foamed adhesive. The adhesive foam may beproduced by mechanical means such as mechanical stirring or agitation,introduction of gases or by chemical means.

[0029] The amount of air dispersed in the adhesive can vary depending onthe particular formulation, but will generally be from about 10% (byvolume) up to about 50% (by volume) or greater.

[0030] The adhesive may be applied by any method known in the art.Typically the particle board is coated with from about 2½ to about 6 wetmils of foamed adhesive, most typically about 3 mils. Preferably, thefoamed adhesive is applied using a roll coater, also referred to in theart as a glue spreader. Top and bottom double sided coaters areadvantageously used in the practice of the invention

[0031] In a preferred method of this invention, pressure is applied in acontinuous process at a temperature of less than about 140° F., mostpreferably about 120° F. to about 140° F. The pressure at which bondingtakes place is generally greater than 20 psi (138 Kpa). Heat may beintroducted by heating elements, or by heating rollers. Typical bondingpressure is no more than 300 psi, although higher pressure is possible.Pressure may be applied to the construction by any suitable means.Preferably, pressure is applied via a roller or by hot pressing. Themost preferred method of applying pressure is via a nip roller.

[0032] The bonding temperatures that may be used in the practice of theinvention are lower than prior art temperatures used when employingunfoamed adhesives and require less power usage in the process, reducedcycle time between successive laminate presses, saves on processingcosts and improves productivity. The method of this invention may besubstantially automated for mass production techniques and utilizes arelatively small amount of foamed adhesive when compared with prior artmethods.

[0033] The invention is further illustrated by the followingnon-limiting example.

EXAMPLE

[0034] An adhesive comprising 54.90% water, 5.00% fully hydrolyzedpolyvinyl alcohol, 20.0% ethylene vinyl acetate (DUR-O-SET), 20.00% clayfiller (Englehart) and 0.10% Kathon LX was prepared by first cooking thepolyvinyl alcohol with the filler in water heated to 200° F. for onehour. After being heated for one hour the adhesive is cooled to atemperature of 120° F. or lower before adding the ethylene vinyl acetateemulsion. Kathon LX was then added as biocide.

[0035] The adhesive prepared as above was foamed to a level of 40% . Thefoamed adhesive was then coated onto an aerated concrete board at acoating weight of 4-5 wet grams per square foot. The paper was thenmated and nipped, then dead stacked under slight pressure for twominutes. After the two minutes, bond strength was measured. A good papertearing bond was found to have been achieved.

[0036] The foamed adhesive was also used to bond paper to aeratedconcrete that had moisture content of 20% . The moisture present camefrom the process of making the aerated concrete. To get 20% moisture inthe lab samples used in this example, the boards were soaked in waterfor one minute, then placed in an oven set at 130° C. for three minutesbefore the facings were bonded as above. Bond strength was thenmeasured. As in the above test, good paper tearing bonds were achieved.

[0037] Many modifications and variations of this invention can be madewithout departing from its spirit and scope, as will be apparent tothose skilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An adhesive comprising water, ethylene vinyl acetate and/or propylenevinyl acetate, and at least one polyvinyl alcohol.
 2. The adhesive ofclaim 1 comprising ethylene vinyl acetate.
 3. The adhesive of claim 1further comprising a filler.
 4. The adhesive of claim 1 wherein thepolyvinyl alcohol is a fully hydrolyzed polyvinyl alcohol.
 5. Theadhesive of claim 1 which is a foamed adhesive.
 6. The foamed adhesiveof claim 5 where the adhesive is foamed from about 20 to about 60%weight per volume.
 7. The adhesive of claim 2 comprising from about 15to about 50% of ethylene vinyl acetate and from about 3 to about 7% of afully hydrolyzed polyvinyl alcohol.
 8. The adhesive of claim 7 which isa foamed adhesive.
 9. The foamed adhesive of claim 8 where the adhesiveis foamed from about 20 to about 60% weight per volume.
 10. An articleof manufacture comprising the adhesive of claim
 1. 11. An article ofmanufacture comprising the adhesive of claim
 8. 12. The article of claim11 which is a wallboard sheet comprising a core having opposing firstand second major surfaces; said core comprising concrete; and at leastone face layer on at least one of the first and second major surfaces ofsaid core, wherein at least one of said face layer is bonded to the corewith said adhesive.
 13. The article of claim 12 wherein the corecomprises aerated concrete.
 14. The article of claim 13 wherein said atleast one face layer comprises paper.
 15. A method for bonding materialstogether which comprises applying the foamed adhesive composition ofclaim 8 to a first substrate, bringing a second substrate in contactwith the adhesive composition applied to the first substrate, andsubjecting the applied composition to conditions which will allow thecomposition to cool and form a set bond.
 16. The method of claim 15wherein one of said first or second substrate is concrete and the otherof said first or second substrate is paper.
 17. The method of claim 16wherein said concrete is aerated concrete.
 18. The method of claim 17wherein adhesive is applied to the aerated concrete substrate.
 19. Themethod of claim 17 wherein adhesive is applied to the paper substrate.20. The method of claim 15 wherein said conditions which will allow thecomposition to cool and form a set bond comprises heat and pressure.